Power supply systems have been used which are configured so that electric power is supplied to a load by a chargeable secondary battery and the secondary battery can be charged as required even during driving of the load. Representatively, such power supply systems are mounted on hybrid cars and electric cars, each of which includes a motor driven using the secondary battery and serving as a vehicular driving force generating source.
In each of such power supply systems, electric power stored in the secondary battery is used as electric power for driving the motor serving as a driving force source, whereas the secondary battery is charged by regenerative electric power generated by the motor and electric power generated by a generator according to rotation of an engine. In such a power supply system, when the secondary battery is overdischarged or overcharged, the battery performance is deteriorated significantly, which may result in a short life thereof. Hence, generally, electric power charged/discharged to/from the secondary battery is controlled based on a battery temperature and an estimated remaining capacity (representatively, SOC: State of charge).
For example, Japanese Patent Laying-Open No. 11-187577 (Patent document 1) discloses a charging/discharging control device for preventing deterioration of a secondary battery resulting from overcharge/overdischarge, by setting a charging power upper limit value and a discharging power upper limit value to values smaller than those at a normal temperature when the battery temperature is equal to or smaller than a predetermined temperature or equal to or greater than the predetermined temperature, in order to charge/discharge with electric power appropriate for the battery's use environment and the battery's state.
Further, Japanese Patent Laying-Open No. 2004-31170 (Patent document 2) discloses a secondary battery internal resistance detecting device capable of highly accurately calculating internal resistance of a secondary battery in consideration of a degree of influence of polarization and a characteristic of a relation between current and voltage. More specifically, it is disclosed that for detection of internal resistance, a polarization index is used as an index representing a polarization state (degree of influence of polarization), which expresses a solution concentration in the vicinity of the electrode by an amount of electric power. In this way, the internal resistance is highly accurately detected in consideration of change in solution concentration in the vicinity of the electrodes caused by charging/discharging as well as an amount of dissipation resulting from dispersion. Further, Patent document 2 describes that the internal resistance of the secondary battery is detected highly accurately and deterioration of the secondary battery is detected from increase in the internal resistance to surely prevent decreased engine startability and the like in advance.
Furthermore, Japanese Patent Laying-Open No. 2000-123886 (Patent document 3) discloses a full charge determining device capable of determining full charge state of a vehicular secondary battery irrespective of an influence of hysterisis. In particular, Patent document 3 discloses that the full charge state is determined by calculating the slope of a line of direct function representing a relation between change in voltage caused by polarization occurring in the battery and a polarization index representing the magnitude of polarization, and comparing for determination the calculated slope with the slope of a line of direct function representing a predetermined relation between the change in voltage upon a full charge state and the polarization index. Patent document 3 also describes that the change in voltage by polarization and the change in concentration of an electrolytic solution at a surface of an electrode are associated with each other.
Further, Japanese Patent Laying-Open No. 2006-42497 (Patent document 4) discloses that control for distributing driving force is optimized among a plurality of motive force sources of a motive force output device in accordance with a local SOC found based on estimated distribution of ion concentration within a secondary battery. A part of the motive force sources generate driving force using electric power supplied from a secondary battery. Specifically, the control for distributing driving force is modified according to a local SOC found based on the distribution of ion concentration at an electrode in the secondary battery as well as comparison with the entire SOC of the entire secondary battery.
Patent document 1: Japanese Patent Laying-Open No. 11-187577
Patent document 2: Japanese Patent Laying-Open No. 2004-31170
Patent document 3: Japanese Patent Laying-Open No. 2000-123886
Patent document 4: Japanese Patent Laying-Open No. 2006-42497